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Questions tagged [rf]

Short for Radio-Frequency. Frequencies at which radiation (intentional or not) plays a role. Typically associated with wireless communications, but also relevant for high-speed PCB design.

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Is there any physical limitation to cell carries sharing the same frequency?

Currently in the U.S. certain companies are granted leases on certain frequencies for cell phone communication. I was discussing with a friend how this allows a company with a lower frequency to get a ...
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0answers
44 views

Has anyone designed a low noise amplifier in the ISM band (24 GHz) using the discrete fet CEL CE3520K3?

I have been trying to design an LNA in the 24 GHz ISM band using CE3520K3. The FET is inherently unstable and one cannot use resistor loading at the input, resistive loading at the output, source ...
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1answer
24 views

How to convert lumped components to TL segments?

I have the following circuit: which I need to implement in Microstrip. For now in order to get the correct results I was using lumped capacitors. But I will need to use Microstrip stubs when ...
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3answers
94 views

Why do carrier waves sound silent on radios?

I was recently reading about and building low-power AM radio transmitters, and read/noticed that when the carrier wave is not yet modulated, the radio receiver goes silent. For example, let's say my ...
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1answer
50 views

What is the major difference between a WiFi and RF Module?

In an interview recently, someone asked me what is the major hardware level difference between a WiFi module (ESP8266) and RF module (nRF24L01+) that I had used in my projects. I mentioned that both ...
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0answers
25 views

RFI protection for a stepper motor controller

I'm building a remote tuning device for a magnetic loop antenna. It will use a stepper motor to turn the shaft on the mag loop's variable capacitor. The electronics will consist primarily of a ...
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2answers
54 views

What equipment would I need to detect and decode a signal coming from a scoreboard remote transmitting at 902 mhz [closed]

Would I be able to use some type of software defined radio receiver on a USB stick (https://www.adafruit.com/product/1497) to detect and decode a scoreboard remote transmitter operating at 902 mhz. ...
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0answers
18 views

Unitary property of scattering matrix

From s-parameter lossless network definition , The sum of the incident powers at all ports is equal to the sum of the reflected powers at all ports. But how do we derive the above unitary property ...
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0answers
33 views

Where to add RF power amplifier [closed]

I am trying to make a SX1262 circuit using this schematic, I have the values for the passives from the BOM already. But I do not understand the schematic very much, where would I place an rf amplifier ...
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1answer
54 views

How to reduce the range of RF sensors to 1.5m? [duplicate]

I have bought four RF sensors from Robokits - Wireless RF serial link 433 MHz +20 dBm 2 Km range. I want to locate one of them with the help other three sensors by the means of triangulation. My ...
4
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2answers
100 views

Strange shapes on the Wi-Fi module PCB

LG has this Wi-Fi module: This is a 2X2 Dual Band AC Wi-Fi / BT module. You will see two folded WiFi antennas on upper side and one bluetooth PCB trace antenna at the lower right side. I found this ...
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0answers
38 views

Unexplained differences in behaviour between U.FL-terminated antenna and SMA-terminated antenna

I would like your opinions/advice regarding an unexplained observation between a U.FL-terminated antenna and an SMA-terminated antenna. Both antennas are from the same manufacturer and normally tuned ...
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5answers
1k views

Why do OOK transmissions have bandwidth?

With on-off keying, you have a single carrier wave at a constant frequency transmitting its presence or absence. Now I understand that the crystal will not be perfect so you will have some minimal ...
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0answers
29 views

ADS VtPulse not working

10nsec Period -> 100 MHz AC Simulation UM ? Where is my pulse signal ? I double checked that I'm in the right cell
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3answers
72 views

BJT Amplifier vs Manufactured RF Mixers

900Mhz Operation This is a BJT mixer design I found on google From my understanding in order to use a BJT amplifier as a mixer you have to be in the 1dB compression point. Question: Am I wrong ? ...
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1answer
52 views

Does a lithium battery make a good ground plane?

A patch antenna I'm using calls for a 50mm x 50mm ground plane under it, mostly to cut multipath reflections in the bottom lobe. Naturally, the closer to the antenna and the more conductive the ground ...
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1answer
143 views

How do I correctly protect my MCU from resetting during a current surge on RF transmission?

I designed a PCB with a SIM868 module for data transmission. On the PCB, the MCU resets randomly on transmission start of the SIM module. On a breadboard setup, it worked just fine, even without caps. ...
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0answers
22 views

Power spectral bandwidth interpretation

I'm developing a LoRa solution that I want to check is compliant with radio spectrum laws in Australia. The radio will transmit at 915Mhz at 22dBm (158mW) with a channel bandwidth of 500Khz, and won't ...
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3answers
56 views

Does data rate increase with channel frequency?

It is commonly said that a higher channel frequency implies a higher data rate. For example, in https://www.howtogeek.com/222249/whats-the-difference-between-2.4-ghz-and-5-ghz-wi-fi-and-which-should-...
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2answers
48 views

Resources on Noise Circuits

Back when I was taking an RFIC design course, I was pretty disappointed by the noise part of the class, specifically calculating the output-referred noise voltage, noise figure of an amplifier, etc. ...
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2answers
41 views

Determining whether signal meets the 12 dB SINAD voltage

The specification for the sensitivity of a certain radio receiver says: Typically 12dB SINAD NBFM for 0.15uV at 145MHz. If I understand correctly, this means that the received radio wave should have a ...
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0answers
15 views

ESP32: Using SENSOR_VP as GPIO

According to the ESP32 Hardware Design Guidelines, in section 2.1.6, they said: If SENSOR_VP and SENSOR_VN are used as GPIOs, while ADC is supported by other pins in the circuit design, users ...
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1answer
83 views

What are the main characteristics of high reactive power RF capacitors?

This question is related to this one. I have to design a high quality factor RF parallel resonant circuit, to be placed in parallel to the output of a medium to high power RF generator. Precisely, ...
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1answer
36 views

What are the units when solving Transmission Line iterativelly?

I would like to know the conductancee,\$C\$, and capacitance,\$G\$, of my lossy transmission line which is configured as an open circuit. In such a case, I know that the expression that defines the ...
4
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2answers
76 views

Reducing the range of a D flip-flop frequency detector

I'm designing a frequency tracking circuit and I came up with a circuit that tracks frequencies from Fclk to Fclk/2: However, it would be very nice if the bandwidth was a bit narrower, from Fclk to ...
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1answer
47 views

Can we install product above FCC test power level declared in certification report

we have a product which has radio of 1W maximum output power , we have sent product for FCC through party lab, and they certified the product with 18 dbm only. So we get the certificate with only 18 ...
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0answers
36 views

Measured doppler shift error biggest on direct flight on target

Following scenario: There is a radar on a plane which emits a CW Signal and outputs the measured doppler shifts from the reflection of a static target. I can see from the data, that the error of the ...
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0answers
28 views

Does feedline of through-hole antennas have to be at the bottom?

Does feedline of through-hole antennas have to be at the bottom of the PCB or is it ok to have it on the top? I don't see why it can't be on the top but I read in Taoglas docs that it should be on the ...
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1answer
97 views

Can wax really improve the performance of a FM transmitter?

Why would the use of wax improve the performance of a FM transmitter? Consider this from the video How to build a FM radio transmitter, at 4 min 14 secs: "Theoretically this helps decrease onboard ...
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1answer
67 views

Bigger GPS antenna better or more efficient?

I have the choice between: 1) 35x35mm GPS antenna 71% efficiency glonass, tested on 70x70 GND plane 60% gps 2) 25x25mm GPS antenna 83% GPS, 84% glonass, tested on 50x50 GND plane I have read ...
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0answers
40 views

Non resonant antenna electrical model

I apologize in advance if my question is too naive or incorrect; I am still very new in the difficult domain of RF and antennas. I know that at the first order, a resonant antenna can be modeled ...
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2answers
77 views

Can I use the same antenna for GSM and RF433 MHz?

I've already designed a PCB with GSM/GPRS chip and also with RF 433MHz receiver only (without transmitter). I would like to know if I can use the same antenna for both GSM/GPRS module and RF 433MHz ...
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2answers
39 views

RF Design - Antenna Feed-line Parameters

I am implementing a BLE device with a chip antenna. The device has already been impedance matched to 50Ω and is ready to be connected to the feedline and antenna. The antenna datasheet has a ...
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2answers
92 views

Why do long cables measured with a VNA show a “drop” in their attenuation curve?

I'm measuring the attenuation of several cables with a VNA (Keysight N5234A). When I measure the attenuation of long cables (10 m, 30 m, 40 m or 50 m) I realize that a "drop" appears at 500MHz (see ...
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1answer
149 views

Why can't we divide the electromagnetic spectrum into arbitrarily many radio frequency bands?

I understand there is concern over the limited amount of wireless spectrum available for allocation but am somewhat confused as to why. Couldn't we just divide the electromagnetic spectrum into as ...
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1answer
25 views

Rf Module Receiver With Pt2272 always gets signal

I am just trying to on and of an led with rf module. I have tried lots of module but my works end up with same result. When I feed my receiver, with led connected to data out, it always powers the ...
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2answers
70 views

differential grounded coplanar waveguide, GND-sig-sig-AVDD instead of GND-sig-sig-GND

I know we can route microstrips on top of both ground and power planes, but can we use Grounded coplanar in this arrangement? bottom is GND In top layer we have one GND and a PWR. All gaps are 0.15mm ...
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1answer
91 views

Unexpected loadline in ADS simulation

NOTE: This question is related to a homework project. I’m designing a PA for the 850-880MHz band. We have quite a lot of freedom for doing that. Only two requirements are specified: The amplifier ...
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1answer
36 views

Comb generator vs. known EMC emitter - different measurements in shielded tent vs. 3 meter chamber

I've got an EMC testing setup of a 1 meter shielded tent, and a very high gain EMC antenna. I'm seeing a phenomena that I can't quite explain. I have a known product that was tested in an accredited ...
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3answers
85 views

Low capacitance value capacitors in LC bandpass filter

I am going to try to build a Butterworth LC bandpass filter. However, using some online calculators result in some very low value capacitors (sub-1pF). I am thinking that the performance will not be ...
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0answers
60 views

Does regularly spaced via stitching contribute to standing waves on an RF PCB?

Should vias be irregularly spaced? Can consistent spacing between ground vias create standing waves. Has anyone ever heard of this? I've been doing this for awhile and I've never heard this and ...
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1answer
60 views

2.4 GHz Chip antenna layout

I am am new to RF design and I need to place a chip antenna due to space limitations. The only antenna that is easily available to me has a very weird layout. There is no physical connection from the ...
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0answers
45 views

Single-frequency AM Receiver?

Previously today, I tried to make an extremely simple AM receiver without a tuner. It didn't really work (I'm still trying to work on it), but I also tried to make an AM receiver that is tuned to one ...
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2answers
23 views

Power Ratings of RF Attenuators In Series

If I connect RF attenuators in series, does the power rating of the attenuator closest to the antenna have to be high enough to handle the expected RF power on its own? Or does the placing attenuators ...
6
votes
1answer
93 views

High Frequency Characteristics of Solder-Filled Vias

If a via gets plugged with solder, does this destroy its ability to pass high frequency (RF noise) currents? Since there is no longer a surface along which the high frequency currents can travel due ...
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1answer
176 views

What's the catch with these JFETs?

I'm designing a low-noise, high-bandwidth (100 MHz) pre-amp using JFETs. The choice for JFETs was because it needs to operate with large source impedances (>10 kΩ). I spent a while looking for a ...
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0answers
56 views

GPS PCB RF Design and Performance Impact

I have designed a vehicle tracker for two-wheelers which is installed in 500 bikes. I am facing an issue with GPS performance (lock percentage is quite low for more than 75% bikes). This makes me ...
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2answers
70 views

RF - sma pth connector impedance matching to cpw

I am designing a 4-Layer PCB with an SMT GPS/GNSS receiver (1575.42 MHz), where it connects to an external antenna through an SMA Connector. I have already done all the calculations of CPWG using ...
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2answers
42 views

coplanar waveguide vs microstrip for gnss and cellular?

coplanar waveguide vs microstrip for gnss and cellular? I read on internet microstrip is better for signals <30Ghz but some gps manufacturer (Delorme) said that coplanar is most efficient so it's ...
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0answers
74 views

Low latency wireless audio transmitter

I am working on a project that requires low latency wireless point to point audio transmission at short distance using a digital transmission technique (ideally 24bit 96khz audio, 30 metre max) at a ...